I bit the bullet and bought one of the products, the [product|IF107-080-3|Unibody Laptop Dual Drive]. While not on the list of compatible Macbook models explicitly, this optical drive bay HDD enclosure worked in my 2 GHz (Early 2009) MacBook 13" (model A1181). I think the key was that this model uses a SATA optical drive, which is the same as the Unibody models. The only issue was that I needed to clip off two of the little plastic pieces to get it to fit into the optical bay.